There is a large body of art dealing with the technology for inserting digital watermarks into images and for reading such watermarks. In general the known techniques for inserting a digital watermark into an image involve changing some property of selected bits or pixels in an images. The pixels or bits are changed in a pattern that represents or carries certain data. The data carried by a digital watermark is often termed the “payload”.
In general digital watermarking technologies seek to accomplish some or all of the following goals or objectives: First, the changes made in an image should not be visible to the normal observer. Second, the changes should be such that they can be detected and the payload can be read by a watermark reading program. Third, actions such as rotating, enlarging or manually handling an image should not prevent the watermark from being detected and read.
The important point relative to the present invention is that in the prior art watermarking technologies the watermark is applied to the image, text, audio, etc which will then carry the watermark. With the present invention, a pattern representing a watermark is deposited on a substrate or screen on which an image will be printed or projected.